Spectral Energy Transfer, Generation of Zonal Flows and Their Role in Confinement Transitions

An overview of recent results related to the physics of turbulent structure generation and their interactions in the H-1 heliac is presented. In particular, the role of zonal flows, or time-varying shear radial electric fields, in anomalous transport and confinement transitions is investigated. It is shown that large-scale coherent structures, including zonal flows, are generated through an inverse energy cascade from the unstable spectral range. Once developed, zonal flows affect other turbulent structures and reduce the particle transport driven by them. The phase randomization of coherent structures by zonal flows is shown to be responsible for reducing the anomalous transport. Zonal flows are also shown to act as precursors during spontaneous low-to-high transitions in H-1.